Characterization of biodegradable microsphere-hydrogel ocular drug delivery system for controlled and extended release of ranibizumab

Purpose: To characterize a biodegradable microsphere-hydrogel drug delivery system (DDS) for controlled and extended release of ranibizumab. Methods: The degradable microsphere-hydrogel DDSs were fabricated by suspending ranibizumab-loaded or blank poly(lactic-co-glycolic acid) microspheres within a poly(ethylene glycol)-co-(L-lactic-acid) diacrylate/N-isopropylacrylamide (PEG-PLLA-DA/NIPAAm) hydrogel. The thermal responsive behavior of various DDS formulations was characterized in terms of volume phase transition temperature (VPTT) and swelling ratios changes from 228C to 428C. The mechanical properties were characterized using rheological methods. Degradability of hydrogels were also examined via wet weight loss. Finally, Iodine-125 was used to radiolabel ranibizumab for characterization of encapsulation efficiency and in vitro release. Results: All DDS formulations investigated were injectable through a 28-gauge needle at room temperature. The VPTT increased with increase of cross-linker concentration. The swelling ratios decreased as temperature increased and were not influenced by presence of microspheres. Rheology data confirmed that increase of cross-linker concentration and microsphere loading made DDS stiffer. Increase of degradable cross-linker concentration facilitated hydrogel in vitro degradation. Controlled release of ranibizumab were achieved for investigated DDS formulations for 6 months; and increased degradable cross-linker concentration produced faster and more complete release. Conclusions: The biodegradable DDSs are suitable for sustained release of ranibizumab. Considering ease of injection, degradability and release of ranibizumab, DDS with 3 mM cross-linker concentration and less than 20 mg/mL microsphere loadings is more favorable for future application. Translational Relevance: The investigated DDS is promising for controlled and extended release of anti-VEGF therapeutics to achieve better treatment regimen in ocular neovascularizations.